[Cashtab] Do not render parenthesis around non-existent NFT tickers

Summary:
A number of NFT collections do not have a ticker, so they are displayed with a mysterious '()'

Only show the parenthesis-wrapping around the ticker for tokens that have a ticker.

Test Plan:
npm test and check screenshots here

before:

after:

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D16804